Dissolution of residual tetrachloroethylene in fractional wettability porous media: correlation development and application

This work explores the dissolution behavior of residual tetrachloroethylene (PCE) in chemically heterogeneous soils. A numerical solute transport simulator, that incorporates rate-limited dissolution and desorption using linear driving force expressions, was developed and applied to analyze soil column dissolution data and to conduct numerical dissolution experiments. Published mass transfer coefficients were unable to accurately predict the observed dissolution of entrapped PCE in fractional wettability porous media (media containing both water- and PCE-wet solid surfaces). A two-parameter power function expression for the lumped mass transfer coefficient was developed and successfully fit to these data. Correlations were then developed for the fitted mass transfer model parameters as a function of wettability and grain size distribution characteristics. The power function model, in conjunction with the parameter correlations, yielded reasonable predictions for long-term dissolution behavior in the more PCE-wetting media. Poorer predictions for the more water-wet materials were attributed to an increased sensitivity of effluent concentration behavior to temporal changes in PCE saturation in these systems. Many of the effluent concentration curves exhibited low and persistent concentration tailing after recovery of the separate phase PCE. This tailing behavior could be adequately modeled by incorporation of rate-limited desorption. Results from numerical experiments indicate that both the magnitude and spatial distribution of wettability can significantly influence PCE dissolution behavior and remediation time.